Retired criminal investigator Dave Harrison claimed the behaviour of the defunct Sunday tabloid could have weakened any potential prosecution and put the public at risk.

Harrison, who worked at Soca between April 2006 July 2008, was part of a Soca surveillance team brought in to work on the Ipswich murders in December 2006.

In written evidence to the inquiry, Harrison said: “I believe that by its actions the News of the World jeopardised the murder inquiry.”

In spoken evidence to Leveson this morning he explained how at a meeting on 18 December the surveillance unit was briefed by branch commander Simon Jennings on the first suspect in the case.

‘At the end of the briefing as part of the intelligence that had been received, we assume by Suffolk constabulary, [we were told] that a News of the World surveillance team had been deployed to identify who we were and where we were based,’said Harrison.

He added: ‘Once we’d been told that there was a surveillance capability looking for us – we didn’t know how many people involved, how many cars, whether it that was one guy stood on a pavement or four of five vehicles – we took that into account during our surveillance activity.

‘So we were always looking for potential surveillance teams.”

They identified surveillance teasm attempting to follow them on at least two occasions, said Harrison.

‘We identified them because they were sat in positions that we would sit in if were doing the same job on the outskirts of Ipswich,’he said, adding: ‘If they knew nothing about surveillance they wouldn’t have got anywhere near us.”

In the briefing Harrison and his team were told those following them were ‘probably ex-special forces soldiers who would have a good inside knowledge of surveillance techniques”.

Sunday Mirror team carried out ‘anti-surveillance manoeuvres’

At a second police briefing, they were told about the Sunday Mirror’s attempts to secure an interview with the first suspect in the case, who was later released without charge following the eventual arrest of killer Steve Wright.

‘We were then told that a Sunday Mirror surveillance team not, not exactly a surveillance team, but some sort of capability that allowed them to pick up the suspect and get them to a place there they could debrief him without us being able to follow him.

‘So it could have been a couple of cars designed with counter-surveillance capability to pick the suspect up and carry him off.”

Asked how police knew it was the Sunday Mirror, he replied: ‘I’ve no idea. I assume it’s the same source as the original briefing.”

Harrison said colleagues in his team watched the first suspect being picked up by a team working for the Sunday Mirror who carried out ‘anti-surveillance manoeuvres’before dropping him off at a hotel to be interviewed

But while he claimed the News of the World’s behaviour potentially harmed the public interest, the same could not be said of the Sunday Mirror.

‘I think that the Sunday Mirror’s objectives were merely to pick the suspect up either without being seen and taking him to an area where he could be debriefed without being followed, so I would exclude them from this comment,’he said.

‘I would make it merely in terms of the News of the World.’

He said there were two ways in which the News of the World had jeopardised the inquiry.

‘A potential risk to public safety’

Firstly, he said murder suspects often return to the scene of the crime before they arrested to dispose of evidence or commit further offences. ‘If whilst doing that they thought they were being followed – they obviously wouldn’t know that it was a legitimate police surveillance team or whether it was a newspaper – if they thought they were being followed they might very well stop what they were doing or not do what they planned to do.

If this evidence was lost this was likely ‘that weakens the prosecution case in the future”.

Secondly, the Soca team was tasked with ensuring that that if the killer intended to commit further murders ‘we were in a position to either stop him or pull resources in to stop him.

‘Again, if our surveillance had been weakened by having to try and avoid other surveillance teams looking for us, if we’d lost the subject he may have gone and committed further murder because we were dealing with something else, we were trying to keep away from other surveillance teams.”

Lord Justice Leveson asked Harrison police inquiries are affected if a journalist interviews a suspect before they are arrested.

He replied: ‘I think the main point would be, if by their actions they had lost us, if we hadn’t been able to follow the suspect because they’d picked him up and taken him off to a hotel for instance, and then left the hotel and dropped him off somewhere… and we weren’t there, that person is not under our control, we’re not fulfilling the objectives that we want, either to protect people from further offences or to gather evidence.

‘So they could easily pick him up, take him to the hotel, lose us, drop him off and he could go and do whatever he wanted without us behind him